PSNs may include unicast and multicast Internet protocol (IP) networks and multiprotocol label switching (MPLS) networks. Routing schemes used on PSNs include unicast and multicast. Unicast is the sending of messages to one network destination host on a PSN. Multicast involves sending message to many network destinations or distribution points (end points). These distribution points are reached by traversing various routers (tree joints).
Troubleshooting unicast IP networks may involve Internet Control Message Protocol (ICMP) including ping and trace tools, which allow the connectivity from point A to point B to be determined. Troubleshooting unicast MPLS networks may involve a version of ping and trace tools for MPLS. In multicast, an mtrace tool on a source transmits to the multicast group to find the last hop before a destination. The mtrace tool then follows the multicast path from destination to source by sending a request packet to each hop using unicast. Using the mtrace tool places a high burden on the source.